But there is a male test like the one for women, and researchers from Womack Army Medical Center in North Carolina recently used it to determine how many men in the U.S. have HPV.

They tested a nationally representative sample of 1868 men between 18 and 59, and it turned out 45.2% of them had genital HPV.

"Male HPV vaccination may have a greater effect on HPV transmission and cancer prevention in men and women than previously estimated," the paper, published in JAMA Oncology, concludes.

The CDC has recommended vaccination for girls starting at age 11 since 2006, but the male vaccine didn't get FDA approval until 2009 and didn't get recommended until 2011.

Even now that it is available, few men are taking advantage of that. The study found that only 10.7% of men eligible for the vaccine have gotten it. Similarly, a 2015 study in Pediatrics found that only 13.9% of boys had completed the three-part vaccine. 34.6% had started it, compared to 60% of girls.